We study how partial monolayers of molecular dipoles at semiconductor/metal interfaces can affect electrical transport across these interfaces, using a series of molecules with systematically varying dipole moment, adsorbed on n-GaAs, prior to Au or Pd metal contact deposition, by indirect evaporation or as "ready-made" pads. From analyses of the molecularly modified surfaces, we find that molecular coverage is poorer on low- than on high-doped n-GaAs. Electrical charge transport across the resulting interfaces was studied by current-voltage-temperature, internal photoemission, and capacitance-voltage measurements. The data were analyzed and compared with numerical simulations of interfaces that present inhomogeneous barriers for electron transport across them. For high-doped GaAs, we confirm that only the former, molecular dipole-dependent barrier is found. Although no clear molecular effects appear to exist with low-doped n-GaAs, those data are well explained by two coexisting barriers for electron transport, one with clear systematic dependence on molecular dipole (molecule-controlled regions) and a constant one (molecule-free regions, pinholes). This explains why directly observable molecular control over the barrier height is found with high-doped GaAs: there, the monolayer pinholes are small enough for their electronic effect not to be felt (they are "pinched off"). We conclude that molecules can control and tailor electronic devices need not form high-quality monolayers, bind chemically to both electrodes, or form multilayers to achieve complete surface coverage. Furthermore, the problem of stability during electron transport is significantly alleviated with molecular control via partial molecule coverage, as most current flows now between, rather than via, the molecules.

Synthetic melanin based metal–insulator–semiconductor devices are fabricated for the first time thanks to silicon surface wettability modification by using dielectric barrier discharge plasma. Ambipolar charge trapping in air and ion drift mechanisms under vacuum are identified by capacitance–voltage hysteresis loops. These results aim to foresee the possible integration of synthetic melanin layers as a novel capacitor in organic polymer based devices.

Characterization: Reflectance Fourier-transform spectra were recorded on a Thermo Nicolet Nexus 670 spectrometer. Ellipsometric measurements of dried brushes were obtained with a custom-built nullellipsometer with a He±Ne laser (632.8 nm) light source and a 70.0 angle of incidence. Atomic force microscopy (AFM) images were obtained by contact mode and tapping mode imaging using V-shaped silicon nitride cantilevers (NanoProbe, Veeco, Santa Barbara, CA; spring constant 0.12 N m ±1 , tip radius 20±60 nm) using a MultiMode scanning probe microscope (SPM) and a Dimension 3100 SPM (Veeco, Santa Barbara, CA). Topographic imaging was performed in air, in water, and in water±MeOH (1:1, vol./vol.) mixtures using a fluid cell. Image forces were kept below 1 nN to minimize compression and damage to polymer brushes. All SEM images were taken at 30 kV (accelerating voltage)

Reproducible electrical contacts to organic molecules are created non-destructively by indirect electron beam evaporation of Pd onto molecular films on cooled substrates. In contrast, directly evaporated contacts damage the molecules seriously. Our conclusions are based on correlating trends in properties of a series of molecules with systematically varying, exposed functional groups, with trends in the electrical behaviour of Pd/molecule/GaAs junctions, where these same molecules are part of the junctions

Eumelanin-type biopolymers have attracted growing interest in the quest for soft bioinspired functional materials for application in organoelectronics. Recently, a metal-insulator-semiconductor device with a good quality interface was produced by spin coating of a com. synthetic eumelanin-like material on a dry plasma-modified silicon surface. As a proof-of-concept step toward the design and implementation of next-generation eumelanin-inspired devices, we report herein an expedient chem. strategy to bestow n-type performance to polydopamine, a highly popular eumelanin-related biopolymer with intrinsic semiconductor behavior, and to tune its elec. properties. The strategy relies on aerial co-oxidn. of dopamine with suitable arom. amines, e.g. 3-aminotyrosine or p-phenylenediamine, leading to good quality black polymeric films. Capacitance-voltage expts. on poly(dopamine/3-aminotyrosine) and poly(dopamine/p-phenylenediamine)-based metal insulator semiconductor devices on p-Si indicated a significant increase in flat band voltage with respect to polydopamine and previous synthetic eumelanin-based diodes. Variations of the flat band voltage under vacuum were obsd. for each device. These results point to polydopamine as a versatile eumelanin-type water-dependent semiconductor platform amenable to fine tuning of its electronic properties through incorporation of π-conjugating arom. amines to tailor functionality